Extract counters from accounts table to account_stats table (#9295)

db/migrate/20181116165755_create_account_stats.rb

@@ -0,0 +1,12 @@
+class CreateAccountStats < ActiveRecord::Migration[5.2]
+  def change
+    create_table :account_stats do |t|
+      t.belongs_to :account, null: false, foreign_key: { on_delete: :cascade }, index: { unique: true }
+      t.bigint :statuses_count, null: false, default: 0
+      t.bigint :following_count, null: false, default: 0
+      t.bigint :followers_count, null: false, default: 0
+
+      t.timestamps
+    end
+  end
+end

db/migrate/20181116173541_copy_account_stats.rb

@@ -0,0 +1,54 @@
+class CopyAccountStats < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def up
+    safety_assured do
+      if supports_upsert?
+        up_fast
+      else
+        up_slow
+      end
+    end
+  end
+
+  def down
+    # Nothing
+  end
+
+  private
+
+  def supports_upsert?
+    version = select_one("SELECT current_setting('server_version_num') AS v")['v'].to_i
+    version >= 90500
+  end
+
+  def up_fast
+    say 'Upsert is available, importing counters using the fast method'
+
+    Account.unscoped.select('id').find_in_batches(batch_size: 5_000) do |accounts|
+      execute <<-SQL.squish
+        INSERT INTO account_stats (account_id, statuses_count, following_count, followers_count, created_at, updated_at)
+        SELECT id, statuses_count, following_count, followers_count, created_at, updated_at
+        FROM accounts
+        WHERE id IN (#{accounts.map(&:id).join(', ')})
+        ON CONFLICT (account_id) DO UPDATE
+        SET statuses_count = EXCLUDED.statuses_count, following_count = EXCLUDED.following_count, followers_count = EXCLUDED.followers_count
+      SQL
+    end
+  end
+
+  def up_slow
+    say 'Upsert is not available in PostgreSQL below 9.5, falling back to slow import of counters'
+
+    # We cannot use bulk INSERT or overarching transactions here because of possible
+    # uniqueness violations that we need to skip over
+    Account.unscoped.select('id, statuses_count, following_count, followers_count, created_at, updated_at').find_each do |account|
+      begin
+        params = [[nil, account.id], [nil, account.statuses_count], [nil, account.following_count], [nil, account.followers_count], [nil, account.created_at], [nil, account.updated_at]]
+        exec_insert('INSERT INTO account_stats (account_id, statuses_count, following_count, followers_count, created_at, updated_at) VALUES ($1, $2, $3, $4, $5, $6)', nil, params)
+      rescue ActiveRecord::RecordNotUnique
+        next
+      end
+    end
+  end
+end

db/post_migrate/20181116184611_copy_account_stats_cleanup.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+class CopyAccountStatsCleanup < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def change
+    safety_assured do
+      remove_column :accounts, :statuses_count, :integer, default: 0, null: false
+      remove_column :accounts, :following_count, :integer, default: 0, null: false
+      remove_column :accounts, :followers_count, :integer, default: 0, null: false
+    end
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2018_10_26_034033) do
+ActiveRecord::Schema.define(version: 2018_11_16_184611) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -56,6 +56,16 @@ ActiveRecord::Schema.define(version: 2018_10_26_034033) do
     t.index ["target_account_id"], name: "index_account_pins_on_target_account_id"
   end
 
+  create_table "account_stats", force: :cascade do |t|
+    t.bigint "account_id", null: false
+    t.bigint "statuses_count", default: 0, null: false
+    t.bigint "following_count", default: 0, null: false
+    t.bigint "followers_count", default: 0, null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["account_id"], name: "index_account_stats_on_account_id", unique: true
+  end
+
   create_table "accounts", force: :cascade do |t|
     t.string "username", default: "", null: false
     t.string "domain"
@@ -85,9 +95,6 @@ ActiveRecord::Schema.define(version: 2018_10_26_034033) do
     t.boolean "suspended", default: false, null: false
     t.boolean "locked", default: false, null: false
     t.string "header_remote_url", default: "", null: false
-    t.integer "statuses_count", default: 0, null: false
-    t.integer "followers_count", default: 0, null: false
-    t.integer "following_count", default: 0, null: false
     t.datetime "last_webfingered_at"
     t.string "inbox_url", default: "", null: false
     t.string "outbox_url", default: "", null: false
@@ -629,6 +636,7 @@ ActiveRecord::Schema.define(version: 2018_10_26_034033) do
   add_foreign_key "account_moderation_notes", "accounts", column: "target_account_id"
   add_foreign_key "account_pins", "accounts", column: "target_account_id", on_delete: :cascade
   add_foreign_key "account_pins", "accounts", on_delete: :cascade
+  add_foreign_key "account_stats", "accounts", on_delete: :cascade
   add_foreign_key "accounts", "accounts", column: "moved_to_account_id", on_delete: :nullify
   add_foreign_key "admin_action_logs", "accounts", on_delete: :cascade
   add_foreign_key "backups", "users", on_delete: :nullify